【c++】线程同步改错题 （互斥体）

题目：

#include <iostream>
#include <windows.h>
#include <tchar.h>

// 我想使用线程，让线程按我制定？的方案执行，但是总失败
// 起床-》吃饭-》工作 -》回家 -》起床
HANDLE mutext1;
HANDLE mutext2;
HANDLE mutext3;
HANDLE mutext4;

DWORD CALLBACK Step1(void* param) {
	while (1) {
		WaitForSingleObject(mutext1, -1); 
		printf("起床\n");
		ReleaseMutex(mutext2);
	}
	return 0;
}
DWORD CALLBACK Step2(void* param) {
	while (1) {
		WaitForSingleObject(mutext2, -1);
		printf("吃饭\n");
		ReleaseMutex(mutext3);
	}
	return 0;
}
DWORD CALLBACK Step3(void* param) {
	while (1) {
		WaitForSingleObject(mutext3, -1);
		printf("工作\n");
		ReleaseMutex(mutext3);
	}

	return 0;
}
DWORD CALLBACK Step4(void* param) {
	while (1) {
		WaitForSingleObject(mutext4, -1);
		printf("回家\n");
		ReleaseMutex(mutext1);
	}

	return 0;
}


int main() {
	mutext1 = CreateMutexW(NULL, FALSE, NULL);
	mutext2 = CreateMutexW(NULL, FALSE, NULL);
	mutext3 = CreateMutexW(NULL, FALSE, NULL);
	mutext4 = CreateMutexW(NULL, FALSE, NULL);

	CreateThread(NULL, NULL, Step1, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step2, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step3, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step4, NULL, NULL, NULL);
	Sleep(50000);
	return 0;
}

错误原因：互斥体只能在自己线程解锁。

解决方案不唯一，用事件也可以实现。

这里还是改互斥体的错误。

#include <iostream>
#include <windows.h>
#include <tchar.h>

// 我想使用线程，让线程按我制定？的方案执行，但是总失败
// 起床-》吃饭-》工作 -》回家 -》起床
HANDLE mutext1;

int step = 0;

// 错误原因:互斥体只能在自己线程中解锁,其他线程解锁无效

DWORD CALLBACK Step1(void* param) {
	while (1) {
		WaitForSingleObject(mutext1, -1); // 等待激发态，并设置为非激发态
		if (step % 4 == 0) {
			step++;
			printf("起床\n");
			Sleep(500);
		}
		ReleaseMutex(mutext1);
	}
	return 0;
}
DWORD CALLBACK Step2(void* param) {
	while (1) {
		WaitForSingleObject(mutext1, -1);
		if (step % 4 == 1) {
			step++;
			printf("吃饭\n");
			Sleep(500);
		}
		ReleaseMutex(mutext1);
	}
	return 0;
}
DWORD CALLBACK Step3(void* param) {
	while (1) {
		WaitForSingleObject(mutext1, -1);
		if (step % 4 == 2) {
			step++;
			printf("工作\n");
			Sleep(500);
		}
		ReleaseMutex(mutext1);
	}

	return 0;
}
DWORD CALLBACK Step4(void* param) {
	while (1) {
		WaitForSingleObject(mutext1, -1);
		if (step % 4 == 3) {
			step++;
			printf("回家\n\n");
			Sleep(500);
		}
		ReleaseMutex(mutext1);
	}

	return 0;
}


int main() {
	mutext1 = CreateMutexW(NULL, FALSE, NULL);
	//mutext2 = CreateMutexW(NULL, FALSE, NULL);
	//mutext3 = CreateMutexW(NULL, FALSE, NULL);
	//mutext4 = CreateMutexW(NULL, FALSE, NULL);

	CreateThread(NULL, NULL, Step1, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step2, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step3, NULL, NULL, NULL);
	CreateThread(NULL, NULL, Step4, NULL, NULL, NULL);
	Sleep(50000);
	return 0;
}

当然要注意的地方，step++ 还没做完，线程立即崩溃，一样还是会有死锁问题，不过不属于题目了。